A method of obtaining high contrast and negative photographic characteristics by adding a hydrazine compound to a silver halide photographic emulsion is disclosed in U.S. Pat. No. 2,419,975. This specification describes that when a hydrazine compound is added to a silver chlorobromide emulsion and development is performed with a developer having as high pH as 12.8, markedly high contrast photographic characteristics (gamma (.gamma.) is more than 10) can be obtained.
Such strong alkali developers having pHs of near 13, however, are unstable because they are easily oxidized by air and thus cannot be stored or used for a long period of time. Furthermore, it is known that dot quality and wide screen range which are sufficient for use in a plate-making process using a contact screen cannot be obtained only by increasing the contrast to such high levels that .gamma. is 10 or more. Furthermore, it is known that in order to obtain sufficient dot quality and wide screen range, infectious development characteristics are necessary which are obtained in developing by the use of an unstable lith developer containing a low concentration of sulfite.
British Pat. No. 1,376,600 discloses a method for obtaining photographic characteristics preferred for reproduction of a dot image or line original, by the use of a stable developer. This specification describes that development of a silver halide light-sensitive element with a developer containing (1) a p-dihydroxybenzene derivative, (2) at least 5 g/l of sulfite ions, and (3) a nitroindazole or nitrobenzimidazole compound provides an image having good dot quality. In accordance with this method, however, the dot quality obtained is inferior to that obtained using the conventional lith developer; although the developer is stabilized more than the lith developer. Thus, this method is still unsatisfactory as a method of producing a dot photographic original for plate-making. Furthermore, the method has the disadvantage that as the concentration of sulfite is increased in order to increase the stability of the developer, the dot quality is markedly deteriorated.
A method which can be used to obtain photographic characteristics preferred for reproduction of a dot image by the use of a stable developer is disclosed in U.S. Pat. No. 4,221,857. This method comprises image-wise exposing a light-sensitive element containing a silver halide emulsion of materially the surface latent image type and an acylhydrazine compound, and then developing the thus-exposed light-sensitive element with dihydroxybenzenes in the presence of polyalkylene oxides.
In accordance with this method, a dot image can be obtained which is increased in intensity to higher levels than that obtained by a combination of the conventional lith photographic light-sensitive element and lith development. Furthermore, the image is free from the fringe effect. This method, however, cannot provide such wide screen range as obtained by the conventional lith development.
More specifically, in order to obtain a low fringe dot image by converting the degree of blackening density into the magnitude of dot area by the use of a contact screen, it is necessary that the continuous gradation of the lith light-sensitive element be sufficiently high. Difference between the logarithmic value of exposure amount to provide blackened area of 5% and the logarithmic value of exposure amount to provide blackened area of 95%, i.e., screen range, is theoretically determined by the density pattern of the contact screen used. Wide screen range is preferred, since when the screen range is wide, gradation of original image can be correctly converted to dot image. In other words, when the screen range is narrow, only a part of gradation of original image is convertd to dot image. The screen range obtained by a combination of the lith photographic light-sensitive element and lith development is generally narrower than the screen range which is theoretically expected. This is due to the fact that the combination of the lith photographic light-sensitive element and lith development is easily subject to the development-inhibiting effect caused by Br.sup..crclbar. ions released from those particles developed during development, a local reduction in pH owing to the development reaction, and so forth. That is, the foregoing development-inhibiting effect is increased as where the development occurs actively. In particular, at highly exposed areas, i.e., areas where the blackening dot area is large, small non-blackening areas between dots are apt to be not developed. As a result the packing of maximum points (dots having the largest blackening area) becomes particularly difficult, and the screen range of the maximum point side is narrowed.
Wide screen range reproductivity is necessary for obtaining a high quality print having good gradation reproductivity. The method as described in U.S. Pat. No. 4,221,857 has the disadvantage that it cannot provide wide screen range comparable to that obtained by the combination of the lith photographic light-sensitive element and lith development. The wide screen range cannot be obtained because the sensitivity to the foregoing local development-inhibiting effect is lower than for the foregoing combination, although it can provide good dot quality.
Furthermore, even with the high contrast negative image as described above, there is a need to further increase graininess.